1. Field of the Invention
This invention relates to lighting units using angled lighting for illuminating channel letters and more particularly to LED based lighting units for illuminating channel letters with angled or side emitting LEDs.
2. Description of the Related Art
Recent developments in LEDs have resulted in devices that are brighter, more efficient and more reliable. LEDs are rugged, consume less power, have a relatively long life (up to 100,000 hours), operate at low voltage, and are 30 to 70% more energy efficient than conventional lights, such as incandescent, neon or fluorescent bulbs. As a result of these developments, LEDs are becoming utilized in many more lighting applications that were previously the realm of incandescent, neon or fluorescent light sources.
Channel letters are commonly found on the outside of buildings and are often used to advertise the name of the business. They are typically constructed of aluminum or plastic housing having the shape of a letter and are approximately 2″ to 5″ deep. The housing has a generally U-shaped cross-section, with the top opening in the housing covered by a colored translucent lens that transmits light from within the housing.
Channel letters are typically illuminated with neon or fluorescent light sources that are mounted within the channel letter housing. Neon and fluorescent lights provide a bright and continuous light source that allows the channel letters to be visible at night. These light sources, however, have a relatively short life (20,000 hours), are fragile, operate at high voltage (7,000 to 15,000 volts for neon) and can consume a relatively large amount of power. Neon bulbs can also experience difficulty with cold starting, which can lead to the bulb's failure.
LEDs are more frequently being used as the light source in different sign applications. U.S. Pat. No. 5,697,175, to Schwartz, discloses a low power illuminated sign that is particularly adapted for use with common EXIT signs over doorways. The back of each sign comprises a reflector with a series of cavities with curved surfaces. Each cavity corresponds to a letter and background area in the sign. LEDs are mounted in the center of the cavities to illuminate the letters or background area. The LEDs are provided on a separate perpendicular circuit board or on a central projection formed in the bottom of the cavities, with light from the LEDs directed outward. The letters and background area of the sign are illuminated by light reflecting forward from the curved surfaces of the cavities, so that the only visible light is from the illumination of the cavities.
U.S. Pat. No. 6,042,248, to Hannah et al., discloses an LED assembly for channel letter illuminating signs having an enclosure/housing covered by a translucent lens. Each sign includes a plurality of track moldings at the base of its enclosure, with the moldings running along the longitudinal axis of the sections of the channel letter. Linear arrays of LEDs are mounted on printed circuit boards (PCBs) that are then mounted in the track moldings. Each track molding can hold two PCBs in parallel with each of the PCBs arranged on a longitudinal edge, with the LEDs directed outward.
LED based channel letter lighting is also available from LumiLEDs, Inc., under part numbers HLCR-KR-R0100 and HLCR-KR99-R0200, which comprises LEDs that are each mounted by insulation displacement connectors (IDC) on two inch centers. The chain of LED modules is then mounted into a bendable clip or rail, each of which is then mounted inside a channel letter to hold the LEDs in place. Power is provided by a combination of an AC/DC mother power supply and a DC/DC daughter power supply. A sensing LED is also included as a temperature and current sensor.
U.S. Pat. Nos. 6,932,495 and 7,241,031, both to Sloan et al., disclose channel letter lighting units and lighting systems utilizing the lighting units. In some embodiments these lighting units can be provided as multiple lighting units interconnected by conductors in a chain so that an electrical signal applied to the chain causes the lighting units to emit light. The chain can be made available to purchasers on different holding devices such as a box, reel or rack. Different lengths of the chain can be utilized for a particular channel letter, with the desired length of chain being cut from the holding device and mounted within the channel letter. Power can then be applied to the chain in the channel letter causing the units to emit light.
Different types of chains can have different numbers of lighting units per a length, or stated differently, a different density of lighting units. These chains are typically sold at a cost per measure of length, and the cost per length is typically greater for lighting systems having higher density. To accommodate the different needs of customers for chains of different densities, many different types of lighting system chains need to be maintained and stored and made available to customers. In some channel letter applications it may be desirable to have different densities of units in different locations. This can require purchasing multiple chains with different densities for the same job.
Each of the lighting units in the chain also has a certain number of LEDs, such as two, four, eight, sixteen, etc., depending on the embodiment. In certain circumstances it may be desirable to have fewer than all the number of LEDs provided on the units, such as in locations where the illumination should be spread. Conventional lighting units, however, offer little flexibility in reducing the number of LEDs in certain ones or all of the LED units in a chain.
Lighting units have been constructed by either placing the LEDs within a molded plastic housing or encasing the entire lighting unit within a sealant without a separate housing. The LEDs are flat or parallel in relation to the lighting unit and facing upwards or directly away from the mounting surface of a lighting unit. This creates a light dispersion pattern which has a higher intensity in the center or over the lighting unit but lower intensity at the sides. Dispersion of the light from these lighting units within the channel letter is important to provide the appearance of even lighting throughout the entire channel letter. An even dispersion serves to provide the appearance that the channel letter is itself lighting up rather than having separate light sources within. Some lighting units incorporate the use of reflectors or a lens over these LEDs to help disperse the light, however these may cause a loss of light output due to the lens or reflector.